Preliminary Results on the Ozonation and Biodegradability of Anionic Surface Agents of Municipal Wastewaters F.J. Beltrán, J.F García, P. Alvarez, L.A. Fernández(1) Chemical Engineering and Energetic Deparment. Extremadura University, Badajoz Spain. 1 - Ozone Research Center, Cuba. Commercial surface agents or surfactants constitute an important fraction of organic content of municipal wastewater. They are harmful for aquatic life and specially undesirable as far as the reuse of treated wastewater is concerned. Presently, anionic surfactants form the group of surface agents of highest application due to their biodegradable character. Thus, among this group one can highlight both the alkyl benzene sulphonates, like ABS and LAS the latter characterized by their linear chain. In spite of their high biodegradability, these compounds are not completely removed in wastewater treatment plants because of the high hydraulic residence time they need. In this work the chemical oxidation of ozone as alternative to degrade sodium sulphate dodecylbenzene (possibly the most representative anionic detergent of the ABS group) is studied. Best conditions achieved correspond to pH 11 in distilled water (after 30 min 82 % conversion of surfactant is obtained with 100 mg/L of ozone dose). In wastewater however conversion has a significant decrease (only 27.5 %) at the same conditions likely due to the competitive effects of other substances for ozone and hydroxyl radicals generated. On the other hand, the influence of preozonation on the biological oxidation of the surfactant in conventional activated sludge system has also been studied. Best results in this case are reached after 4 weeks and with 100 mg/L of ozone dose. At these conditions and starting with 1500 mg/L VSS in prepared wastewater (300 mg/L COD) batch mode after 12 hours biological oxidation performance of surfactants increased about 35.7 % with respect to the non ozonated treatment. Source: 2nd International Symposium on Ozone Applications Havana, Cuba - Mach 24-26, 1997.